The present invention relates to a roller-type mower provided with a rotatable drum or roller with surface cutting members, or one continuous helical cutting blade, provided for rotation at a speed required for unrestricted cutting.
Roller-type mowers of the above-described type are used as attachment-type mowers for tractors or as auto-travelling or manually pushed mowers for gardens, golf lawns, fields, or the like.
The known roller-type mowers entail a couple of disadvantages which will be described in the following:
It is commonly known that in mowing devices rotating about a horizontal axis, the percentage of uncut or incompletely cut grass blades increases initially only slightly but later on to a much higher degree as the angle of inclination between the cutting blade and the axis of rotation becomes larger. FIG. 15 illustrates an example of this fact wherein the interrelationship between the cutting energy required for cutting and the angle of inclination .alpha. of the cutter blade is illustrated. A major reduction of the cut quality will arise with a blunt cutting blade at a comparatively small angle of inclination of some 30.degree..
The reason why a helical mower with a slight inclination .alpha. of the helical smooth cutting blade (and thus with a wide angle of inclination) will fail to produce clean cuts is that the helix pushes the stalks to be mowed to the side rather than cutting them.
FIG. 15 moreover illustrates that with the angle of inclination .alpha. increasing, the required cutting energy is first reduced, which means that a dragging cut with lower power consumption will arise.
A mowing helix with a great inclination operates on a smaller angle of inclination .alpha., which may be compared to a beating mower or a beating chopper for field application. Here the beaters hit the stalks approximately at right angles to beat them off. In accordance with the cycloidal mowing path, which is the more cycloidal the higher the travelling speed, the upright stalks are beaten off in comma-shaped sections a.sub.1, a.sub.2 ; . . . (see FIG. 17). The motion of beating the upright stalks from the top to the bottom continues in accordance with the cycloidal paths of the mowing tools, becoming more and more effective, until the stubble height is reached. The stalks are thus cut into multiple pieces over their length, with pieces being so reduced in length that they drop into the stubbles and can no longer be picked up. The multiple severing of the upright stalks also requires an appropriate power supply. When the mowed material is not ejected directly to the rear end, but rather against the stalks still standing, the stalks will also be shortened. Then a stock of mowed material will be formed ahead of the rotor, which the mowing helix partly cuts off and removes even though it increases the volume of the freshly mowed material. The roller-type stock of material ahead of the cutting rotor may also press the fine blades of grass, or beets to be mowed, to such an extent that it will then be seized by the mowing tools only partly. This results in an undesirable stubble height.
In accordance with the foregoing explanation, the power consumption and unfortunately the quality of cut (uniform stubble height) is impaired by a smooth cutting blade with a decreasing inclination of the helix.
With a serrated helix, the inclination of the cutting tooth flank is theoretically decisive for the quality of cut and the power consumption, as well as for the reduction of the natural length of the stalks. The inclination of the helix, however, is relevant also for swath formation, or generally for the axial transport of the mowed material through the mowing helix itself. As can be taken from the laid-open German Patent Application DE 36 35 925 A1, (which corresponds to U.S. Ser. No. 221,255 filed June 22, 1988), the angle of inclination of the mowing helix must not exceed the tangent of the frictional angle of the mowed material (sliding condition).
There is also the particular disadvantage that the cutting blades of roller-type mowers, which extend continuously over the mowing width, become blunt within a relatively short time as stones slide along these blades. The stones are obviously not passed through to the rear end quickly enough. Serrated cutting blades, which provide for a cleaner cut than do smooth cutting blades, are prone to bend whenever stones hit them. As has been set out above, cut leaves and blades may easily get stuck between the teeth.
At a marginal zone of the cutting members, which is inclined to the axis of rotation, it is easily possible that clots of soil will adhere there and reduce the cutting ability.
The present invention is based on the problem of designing the cutting blades of roller in such a way that foreign matter will be easily passed through the cutting blades. This results in long service life, the blades will remain well sharpened for a long time and the adherence of clots of soil will be avoided. Whenever possible, a slight regrinding effect should be achievable on the cutting members in the machine. According to the present invention, with a helical mower with a serrated cutting blade, the reduction of the natural length of the stalks or blades during mowing should be kept as small as possible while providing for clean stubble cutting.
According to the present invention, known cutting blades, which rotate on the surface at a low or even a major inclination, are segmented so as to allow for the passage of foreign matter such as stones, etc. At the same time, the cutting blades are staggered in the direction of rotation, while the cutting segments themselves are intermeshed in a specific geometrical arrangement. To this end, a plurality of separate cutting members is provided on the surface. Each member is pitched at an angle from the axis of rotation, or is of a helical design. Moreover the mutually spaced cutting members overlap each other in the direction of travel. Shorter segmented and mutually staggered helical segments provide for better passage of foreign matter.
A better cutting result, i.e. neatly cut stubbles with a minimum reduction of the natural length of the stalks or blades, will be achieved in accordance with the present invention due to the fact that in a serrated cutting edge, the helix is designed with an inclination so high that it will initially bend the upper portions of the stalks to the side and will then sever the stalks at the designed stubble height with the inclined tooth flanks in the lower section. The angle of inclination of the tooth flanks is so selected that the stalks may not slip off the cutting blade at the stubble height. According to the present invention, this is achieved by having the angle of inclination (.alpha.) of the obliquely or helically pitched cutting members smaller than 30.degree. and the angle of inclination (.beta.) of the flanks effective for cutting in the forward direction greater than 20.degree., while the angle of inclination .GAMMA.' of the cutting blade, relative to the axis, exceeds 60.degree..
It was a surprise to find that a mowing helix with a serration and a small inclination angle .alpha. of the helix, whose effective lines of cut are inclined only at a small angle .beta. and which does not provide for a lateral deviation of the stalks will not result in beat-off of the upper stalk segment. In such a case, the tooth tips obviously have the effect of a quasi-continuous cutting blade at the outer periphery of the helix, which permits the passage of the stalks in the upper stalk section with a relatively small bending resistance, but prevents them from entering the tooth gaps. Only in the region close to the ground will this happen with the increasing bending resistance, so that the cut may be performed. The angle of inclination .alpha. of the helix, which is to be selected accordingly, and the angle of inclination .beta. of the cutting tooth flank are determined by the properties of the material to be mowed.
As far as stalk material is concerned, it may be stated that the angle of inclination .alpha. of a helix with a serrated cutting blade, must be below the frictional angle .mu.. With a frictional value of .mu.=0.5 for fresh material, a frictional angle below 30.degree. will arise. This ensures an axial transport of the mowed material, which is required for swath formation. The angle of inclination .beta. of the effective tooth flanks should then exceed 20.degree. so as to ensure that leaves and stalk fibers will not get caught and that the teeth will retain their cutting ability.
Depending on the nature of the material to be cut, and on the environment in which the material is to be cut, these inventive features may either be combined with each other, or applied separately. It is possible, for instance, to provide cutting members on a drum that are separated from each other and pitched at a angle relative to their axis of rotation and with a cutting blade designed as a continuous helix which is pitched less than 30.degree. and inclined with respect to the flanks of the cutting blades at an angle greater than 20.degree. and wherein the angle of the cutting blade with respect to the rotary axis of the mower exceeds 60.degree.. With meadows full of stones, the specific helix design is not necessary. However, when the mower is to be used on a soil including only a small number of stones, such as on the green of golf courses, the continuous helix described above is desirable.
Provisions are also made to the effect that the marginal zone of the continuous cutting blade, or of the individual cutting members, will enclose an angle with the axis of rotation of the mower.
Moreover, the individual cutting segments may be suspended to oscillate so that the mower is suitable for application on very stony meadows.
An improved passage of stones will be achieved when the cutting members are disks, pitched obliquely with respect to the direction of travel and wherein the rims of these disks are designed as cutting edges.
The service life of the cutting edge with a good quality of cut will be improved by providing a specific undulation of the cutting blade. A serration can be embossed or cut into the outer marginal zone of a helical segment or the rim of a disk. The effective line of cut of the individual tooth is inclined relative to the axis of rotation so that stalks or leaves may not get stuck. Relative to the peripheral direction, the tooth is pointed, which results in an unproblematic and clean cut. The combination of individual teeth contributes to a long service life.
An improvement which prevents the necessity for multiple cutting is obtained by having a light apron disposed near and ahead of the helical rotor, which apron is made to lie on the material to be cut, and bends the material in the direction of travel as well as preventing the mowed material from being ejected in a forward direction. In mowing technology, deep-reaching fixed metal sheet projections or rollers are known which bend the material still to be cut in the forward direction. They do not conform to the density of the stalks or blades of material to be cut, so that the mowed blades must be torn through and out of the mowing tools under the deposit areas of these bend-down elements. Such arrangements result in a partial second cut of the stalks and blades already mowed. The known protective cloths in drum- and disk-type mowers fail to produce this effect, since the multiple cut problem is not involved in such mowing principles. An active transport of the mowed material out of the cutting region can be achieved by a driven roller which is disposed directly ahead of the helical rotor.
Longitudinal bars may be disposed on the drum or the roller of the helical mower so as to promote the rapid material transport. Moreover, provisions have been made to achieve a detachment of the mowed material in the front region of the mowing drum by use of a hood beginning to rise ahead of the center of the helical mower. A slight sector of contact with the mowing helix reduces the danger of multiple cutting. The hood adds the possibility of a turning effect for the material by the hood dome so that the stream of cut stalks will be deposited on the ground either with the stalk ends on the top, or in an irregular bunch, so that the cut material will dry more rapidly.
Specifically when home greens or golf courses are to be mowed or where a very clean and a maximum smooth cut is desirable, it is recommended to operate with ground cutting blades which, in their turn, provide for a rather low inclination of the helix. Because of this, the cutting blade of the helix should be easily replaceable. Such is accomplished wherein the cutting blade is band-shaped and so attached onto a helical supporting body that it will fully rest upon the latter. This cutting band typically includes an angle of .GAMMA.'.perspectiveto.60.degree. so that soil clots and stalk or blade residues may not accumulate. When removed and spread, this band thus constitutes a circular ring, or a segment thereof, whose radii are defined by the inclination of the helix.
A helical supporting body which carries the band is Provided with a stripshaped surface on which the band may rest. When a straight elastic strip of band with the same pitch is wound onto a cylinder it will "fully rest" on the side, i.e. without any gap. In this design, the band rests on a collar so that it is suitable to absorb the axial component of the cutting force.
Towards the cutting side, the helical bar of the supporting body which carries the band, is pitched at some 60.degree. relative to the axis of rotation such that segments of stalks, blades and leaves as well as soil clots may slip off.
With a serrated cutting edge of the band, the inclined helical bar opens at the root of the teeth so that only the teeth are projecting. The teeth may be slightly raised by 20.degree. from a paraxial line so that the teeth themselves may be ground or trued according to the generally known grinding method by a sharpening stone being moved to and fro with the rotor running.
It is also possible, of course, with a different design of the cutting members, to grind the cutting blade with the rotor running by feeding a grinding bar (corundum bar) or stone moved to and fro across the blade.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.